This invention relates to a method for processing returns from oil and gas wells that have been treated with introduced fluids. Introduced fluids commonly used in oil and gas wells include acid stimulation packages, hydraulic fracturing fluids, completion fluids, drilling fluids, and combinations of these.
A. Acid Stimulation Package
Acid stimulation packages are introduced fluids that are designed to remove formation and wellbore damage to improve the productivity of a hydrocarbon producing well. These packages frequently contain acid and other additives. The acid may be mineral acids such as hydrochloric acid or hydrofluoric acid or the acid may be an organic acid such as acetic acid. Combinations of hydrochloric acid and hydrofluoric acid may be used and combinations of mineral acids with organic acids may be used. Other additives that may be present in the acid package include corrosion inhibitors, surfactants, anti-sludging agents, non-emulsifiers, mutual solvents and gelling agents. These additives are present to provide additional properties to the acid package, such as corrosion protection for metal surfaces, improved wettability of formation surfaces, to prevent formation of sludges from the interaction of the acid with the hydrocarbon phase, to prevent emulsions from forming downhole, and to enable the package to be formulated into a stable solution.
B. Hydraulic Fracturing Fluid
Hydraulic fracturing is applied to break down the formation by pumping introduced fluids under high pressure to improve the productivity of the hydrocarbon producing zone. Hydraulic fracturing fluids may contain a variety of additives such as clay stabilizers to prevent clay swelling and fines migration, gelling agents to increase viscosity, proppants to remain in the formation and create a permeable channel in the fracture and other additives as may be required.
C. Completion Fluids
Completion fluids are introduced fluids that are used during final completion operations in drilling a new well. These fluids frequently are weighted brines containing inorganic salts to increase the density of the fluid such as metal salts of halogens, i.e. zinc bromide, calcium chloride, etc. Completion fluids frequently may contain gelling agents to increase viscosity.
D. Drilling Fluids
Drilling fluids are introduced fluids that are used during the drilling process to maintain pressure against the producing formation to prevent blowouts, to transport drill cuttings to the surface and to lubricate and cool the rock drilling bit. These fluids may contain weighting agents, viscosity modifiers, polymeric additives and clay stabilizers. Clays such as bentonite are frequently added to drilling fluids and the fluids are commonly referred to as drilling muds.
Using introduced fluids may cause the formation of sludge/emulsion. Artificial sludge/emulsion formation may be minimal on initial flowback, but as production fluids mix downhole with the introduced fluids, additional sludge/emulsion may be formed. Sludge/emulsion formation may also occur when the introduced fluid flowback is commingled with production from other wells.
If an artificially induced sludge/emulsion problem is not resolved promptly, it will cause a malfunction in the crude oil dehydration treating system. This type of malfunction is commonly referred to as a system upset. A typical crude oil dehydration treating system includes a separator, free water knockout, heater treater or chemelectric, and/or air flotation unit, etc. Crude oil dehydration treating systems are typically used to reduce the basic sediment, and water (BSandW) of crude oil to a certain acceptable level specified by a crude oil purchaser. Crude oil purchasers are often pipeline companies. The level of BSandW typically specified by purchasers is less than 1%.
When a system upset occurs in the treating system two problems occur. First, the required basic silt, sediment, and water level cannot be achieved to meet a purchaser""s specifications. Second, high levels of oil and other organic material remain in the resulting water which prevents the resulting water from meeting water quality specifications. The chemicals and systems used for normal oil water separation and processing are not adequate to resolve the sludge/emulsion formed as a result of the use of introduced fluids in oil and gas wells.
To date, the typical method of coping with the possibility of a system upset is to mechanically remove the sludge/emulsion by catching it in large storage tanks. Removal and treatment of sludge/emulsion is a major operational cost for producers. This is particularly true for offshore wells because the sludge/emulsion must be collected, stored, and transported to shore for treatment and disposal.
There is a need for an efficient process to: (1) resolve the sludge/emulsion formed when introduced fluids are added to oil and gas wells; and (2) clean the resulting water sufficiently to meet environmental regulations for disposal. The present invention meets this need.
One embodiment of the present invention is directed to a method for treating sludge/emulsion formed as a result of treating oil and gas wells with introduced fluids. Introduced fluids include acid stimulation packages, hydraulic fracturing fluids, completion fluids, and drilling fluids either individually or in combination. Sludge/emulsions may be treated by adding one or more adjunct chemicals in combination with an emulsion breaker. The adjunct chemicals may be selected from a group of chemicals consisting of iron-control chemicals, scale-control chemicals, and paraffin-control chemicals. The iron-control chemicals may be selected from a group of chemicals consisting of thioglycolic acid, sodium ethylenediaminetetraacetic acid, potassium ethylenediaminetetraacetic acid, sodium hydroxyethylethylenediaminetetraacetic acid, potassium hydroxyethylethylenediaminetetraacetic acid, sodium nitrilotriacetic acid, potassium nitrilotriacetic acid, sodium bisulfite, ammonium bisulfite, and potassium bisulfite. The scale-control chemicals comprise organic phosphonates, such as hydroxyethylidienediphosphonic acid, aminotri(methylenephosphonic acid), phosphonobutanetricarboxylic acid, phosphoric acid derivatives of polyamines and organic phosphate esters, copolymers containing phosphino groups, polyacrylic acid, copolymers of polyacrylic acid with sulfonated maleic acid and copolymers of polyacrylic acid with sulfonated comonomers. The paraffin-control chemicals may be selected from a group of chemicals consisting of ethylenevinylacetate copolymers, styrene maleic anhydride copolymers, polyacrylic esters of C20 alcohol, dodecylbenzylsulfonic acid, dialkylbenzylsulfonic acid, polyoxyalkylenealkylphenolformaldehyde resins, alkyl acrylates, alkyl methacrylates, alkyl esters, and polyoxyalkylene copolymers.
The emulsion breaker may be water-dispersible and is added to the sludge/emulsion in an amount sufficient to separate the sludge/emulsion into a water phase and an oil phase. The resulting water can be further treated with a water clarifier and then a separation process that comprises prefiltering the water and passing the water through a resin media. The resin media comprises a macroreticular resin. The water clarifier may be added in an amount sufficient to clarify the water to contain less than about 29 milligrams/liter (mg/L) of organic material, a purity adequate for discharge at sea. Such discharge would not create a sheen on the water. The water clarifier may include organic polymers such as polyacrylic acid, acrylic acid based polymers, acrylamide based polymers, polymerized amines, alkanolamines, thiocarbamates cationic polymers or inorganic salts such as alum, aluminum chloride, or aluminum chlorohydrate.
Another embodiment of the invention comprises a sludge/emulsion treatment composition comprising a water-dispersible emulsion breaker and adjunct chemicals comprising iron-control chemicals, scale control chemicals, or paraffin-control chemicals or combinations of iron-control chemicals, scale control chemicals, and paraffin-control chemicals. The iron-control chemicals of the composition comprise thioglycolic acid, sodium ethylenediaminetetraacetic acid, potassium ethylenediaminetetraacetic acid, sodium hydroxyethylethylenediaminetetraacetic acid, potassium hydroxyethylethylenediaminetetraacetic acid, sodium nitrilotriacetic acid, potassium nitrilotriacetic acid, sodium bisulfite, ammonium bisulfite, or potassium bisulfite. The scale-control chemicals comprise organic phosphonates, such as hydroxyethylidienediphosphonic acid, aminotri(methylenephosphonic acid), phosphonobutanetricarboxylic acid, or phosphonic acid derivatives of polyamines, and organic phosphate esters, copolymers containing phosphino groups, polyacrylic acid, copolymers of polyacrylic acid with sulfonated maleic acid and copolymers of polyacrylic acid with sulfonated comonomers. The paraffin-control chemicals comprise ethylenevinylacetate copolymers, styrene maleic anhydride copolymers, polyacrylic esters of C20 alcohol, dodecylbenzylsulfonic acid, dialkylbenzylsulfonic acid, polyoxyalkylenealkylphenolformaldehyde resins, alkyl acrylates, alkyl methacrylates, alkyl esters, or polyoxyalkylene copolymers.